Automatic choke



Feb. 7, 1961 s TL 2,970,825

AUTOMATIC CHOKE Filed Feb. 3, 1958 '2 Sheets-Sheet 1 INVENTOR.

E 4 w mm 'M/IP/O/VL S/wnzy M. L. SMITLEY AUTOMATIC CHOKE Feb. 7, '1961 2Sheets-Sheet 2 Filed Feb. 3, 1958 INVENTOR. 4442/04 1. 624/715) Arrow 5yAUTOMATIC CHOKE Marion L. Smitley, Huntington Woods, Mich, assignor toHolley Carburetor Company, Van Dyke, Mich., a corporation of MichiganFiled Feb. 3, 1958, Ser. No. 712,717

7 Claims. (Cl. 261-144) This invention relates generally-a carburetorsfor internal combustion engines and more specifically to means forautomatically operating the choking mechanism within the carburetor.

Most carburetors of present design employ a coil-type thermostaticbimetal for controLing the amount of choke opening according totemperature. They also use a manifold vacuum responsive piston forinitially opening the choke a predetermined degree when the cold enginestarts and becomes self-sustaining. These pistons use vacuum by-passmeans, such as slots or ports which are opened or closed by the positionof the piston, in order to control the extent of their movement.

Such systems have proved to be unsatisfactory because even though theamount of vacuum acting on the piston has been substantially reduced bythe bypass means there remains a sufiicient degree of vacuum enablingthe piston to exert a continual torque against the force of the bimetal,thereby seriously affecting the proper functioning of the choke valve.

Another serious deficiency of present carburetors is that there are nomeans for adjusting the amount of initial choke opening, due to thepiston, according to the ambient temperature. As a result, this chokeopens the same amount (for all practical purposes), regardless ofwhether the ambient temperature is 75 F. or 30 F., for example. Becauseof this, the carburetors deliver a mixture which is either too lean ortoo rich (depending on their original calibrations and settings) duringcertain seasons of the year.

The invention as hereinafter disclosed is directly concerned with theseproblems.

Accordingly an object of the invention is to provide means for reducingthe torque of the choke vacuum pis ton to an absolute zero once itsfunction has been performed.

Another object of the invention is generally to provide means forvarying the degree of initial choke opening once the engine starts; morespecifically, the object is to provide means for automatically varyingthe degree of initial choke opening in accordance with the ambienttemperature once the engine becomes self-sustaining.

Other objects and advantages will become apparent when reference is madeto the accompanying drawings in which:

Figure l is a perspective view illustrating generally, a carburetorembodying invention.

Figure 2 is a fragmentary perspective expoded view illustrating thedetails of construction of the left-hand portion of Figure 1.

Figure'3 is an enlarged fragmentary sectional view illustrating ingreater detailthe piston and associated elements shown by Figure 2.

Figure 4 is an enlarged view illustrating some of the elements withinthe vacuum cylinder shown by Figure 3.

"invention.

Referring to the drawings in greater detail, Figure 1 illustrates acarburetor 10 having a throttle body 12, an air intake 14 with inductionpassages therethrough adapted to be influenced by a choke valve 16,which is operatively connected by means of arms 18 and 20 and link 22 tothe automatic choke control 24.

Figure 2 illustrates a housing 26, suitably secured as by screws 28 tothe corburetor 10, having a cylinder 30 formed therein containing apiston 32 Which is connected through a linkage 34 to the choke lever 36.A shaft 38, extending through and rotatable in one wall of the housing26, has secured to it at one end thereof the choke lever 36 and at itsother end secured to it lever 20 (Figure 1). The choke lever 36 has anoutwardly extending projection 40 which is adapted to coact with thefree end 42 of thermostatic element 44 through an arcuate opening 46 inthe housing cover plate 48.

The thermostatic housing 50 has a shaft located centrally Within andrigidly secured to it to anchor the other end of the thermostaticelement 44. Any suitable means such as the clamping ring 52 may beemployed to holdthe cover plate 48 and housing 50 in alignment with andagainst the housing 26. The ring 52 may be secured by means of screws 54and cooperating threaded portions 56.

Conduit 58 communicates between a source of heated air and the chamberformed generally by cover plate 48 and housing 50. Its purpose is todeliver air, which is at a temperature indicative of engine temperature,to the thermostatic element 44 in order that the element may react to itand change the position of the choke valve 16 accordingly.

Conduit 6t) communicates generally between the cylinder 30 and a sourceof engine manifold vacuum in such a manner so as to draw air throughconduit 53 and cause movement of the piston 32 in a direction so as toresult in clockwise rotation of lever 36.

Figure 3 illustrates in greater detail, the details of the choke vacuumpiston 32 and cylinder 30. The piston is connected to a linkage 34 bymeans of a pin 62; the opposite end of the link 34 is operativelyconnected to lever 36 by means of pin 64 which is retained within lever36 and slideable within the lostmotion producing-slotoo of link 34. e it V A thermostatically controlled abutment 68' is located at thesubstantially closed end of cylinder 30 and is thus adapted to limit themaximum movement of the vacuum piston 32. This abutment, as illustratedingreater detail in Figure 4, is generally comprised of shaft 79 havingone end thereof secured to the closed'end of cylinder 30 and other endthereof threaded with atrelatively fast acting coarsethread. A sleeve 72having an internally threaded portion 74 coacting with a threadedportion 76 of shaft 70 has a gene-rally slotted-like indentation 78 intowhich one end 30 of a thermostatic element 82-is suitably secured. Theother end 840i the thermostat 82 may be secured to a rod 86 in agenerally loop-like manner by passing it through a slot 88 within therod 86. The rod 86 is in turn rigidly secured at its opposite end to theclosed end of cylinder 30.

Operation of invention Assuming, for the purpose of illustration, thatthe engine is cold and is being cranked, the thermostatic element 44will be in its unwound condition thereby causing its end 42 to positionprojection 40 of lever 36 in its extreme counter-clockwise position. Thelever 36 being secured to shaft 38 rotates theshaft and arm 20, which issecured to it counter-clockwise thereby causing the choke valve toassume a position which substantially closes on the-flow of air throughthe carburetor induction passage; All of these elements will continue tooccupy these respective positions while the engine is being cranked.

As soon as the engine fires and becomes self-sustaining, manifold vacuumrises to a value sufficient to move the vacuum piston downwardly againstthe abutment 68 in opposition to the force of thermostat 44. This may beaccomplished by means of suitable conduitry which causes the open end ofpiston 30 to be subjected to substantially atmospheric pressure whilethe closed end of the piston "is subjected to manifold vacuum. As theengine continues to run, air is drawn from a suitable stove throughconduits 58, 89 and 90, through an orifice 92 in cover plate 48, intothe chamber formed by the housing 5i and cover plate 48. The air thenwarms the thermostat 4d and passes into the chamber formed by housing 26and cover plate 48 through the arcuate opening 46 within the coverplate. The air is then drawn through an orifice 93, which has arestriction 94 therein communicating with conduit 96, which leads fromthe cylinder 30 to conduits 98 and 60 which are in turn connected to asource of manifold vacuum.

From the foregoing, it is evident that as soon as the engine starts torun the vacuum piston 32 by virtue of its movement causes the chokevalve 16 to open some desired and predetermined amount. However, theamount of this opening, in order that optimum operating characteristicscan be achieved, should be varied in accordance with the ambienttemperature. That is, if the ambient temperature were 0 F. the chokeshould possibly be opened only five degrees, whereas if the ambienttemperature were 65 F. the choke might have to be opened fifteendegrees. These variationsof initial choke opening are necessary in orderto deliver a richer fuel-air ratio when the ambient temperature isrelatively low.

The above described variations are made possible with the use of thisinvention. Because no air is drawn into the cylinder 30, the thermostat82 will respond to the ambient temperature. When the thermostat 82 iscold, it will wind causing sleeve 72 to rotate on the threaded portionof shaft 70 and move away from the closed end of the cylinder. This willresult'in the piston 32 having a shorter stroke and consequently resultin the choke valve 16 being opened a lesser amount when the enginestarts.

Once the piston has moved so as to be held against the sleeve 72 of theabutment 68, no further torque due to manifold vacuum will beexperienced at the lever 36 or choke valve 16. From this point on allregulation of choke valve position is accomplished by the thermostat 44.The slot 66 in the linkage 34 is providedso that further movement of thechoke valve as regulated by the thermostat, will not be prohibitedbecause of the piston 32 being held against the abutment 68. t

From the foregoing it will be apparent that superior regulation of thechoke valve will be obtained because any adverse effects of the vacuumpiston are removed by having it abut against a stop which not onlyremoves any undesirable torque but also determines the correct amount ofinitial choke opening in accordance with ambient temperature.

It is, however, evident that the abutment 68 could be replaced by asolid abutment, as compared to 68 whose length is regulated by athermostatic element 82. If such a modification were employed in a chokemechanism, the undesirable torque created by the vacuum piston would beremoved. Even though there would be no correction of initial chokeopening determined by ambient temperature, the resulting choke valveaction would still be more accurately correlated to engine requirementsthan those chokes of present construction.

Other modifications may be made without'exceeding the scope of theinvention, as defined by the attached claims.

What I claim as my invention is:

1. In a carburetor, a choke valve, a. source of suction, temperatureresponsive means influencing the position of the choke valve,pressure'responsive means communicating with the source of suctionoperatively connected to said choke valve, and positive abutment meansfor limiting theamount of choke movement due to said pressure responsivemeans, and second temperature responsive means for adjustablypositioning said abutment means.

2. In a carburetor for an internal combustion engine having a chokevalve mounted therein, an automatic choke device, comprising athermostatic control for said choke valve, pressure responsive meansoperative when the engine starts to move said choke valve in the openingdirection, and additional temperature responsive means for limiting theamount of movement of said pressure responsive means.

3. In a carburetor for internal combustion engines, a choke valve, meansincluding a heat responsive device to close said choke valve at lowtemperatures, a device responsive to engine suction for causing at leasta partial opening of said chokevalve against the tension of said heatresponsive devide upon starting of the engine, and abutment meansassociated with said suction responsive device adapted to limit theamount of choke opening due to said suction responsive device.

4. A mixture control for internal combustion engines comprising, acarburetor, a choke valve, thermostatic means for closing said chokevalve at low temperatures, pressure responsive means coacting with saidtemperature responsive means adapted to initially open said choke valveupon starting of the engine, abutment means cooperating with saidpressure responsive means and adapted to positively limit said initialchoke movement, and lost motion connecting means connected to saidpressure responsive means for providing for the exclusive control of thechoke valve by said thermostatic means for all choke valve movementsbeyond said initial choke movement.

5. A control mechanism for an internal combustion engine carburetorhaving a pressure responsive choke valve comprising, a thermostattensioned for variably opposing the opening of the choke valve as afunction of temperature, said thermostat being so constructed andarranged as to initially oppose the choke movement with maximum tensionand being rendered ineffective to op pose further choke movement afternormal operating tem perature is attained, pressure responsive meansopposing said thermostat when said engine is started, limit means forrendering said pressure responsive means ineffective before normalengine operating temperatures are reached, and a one-way connectinglinkage cooperating with said thermostat and said pressure responsivemeans for providing choke control by said thermostat.

6. In a carburetor having a choke valve therein, an automatic chokecontrol device comprising, a choke shaft secured to said valve, a membersecured to said shaft and adapted to be rotated therewith, a housing, asecond shaft mounted through one side of said housing and adapted to berotated therein, an arm secured to one end of said second shaftexternally of said housing so as to be rotatable therewith, meansconnecting said member with said arm, a cylinder open at one end andsubstantially closed at its other end, a piston in said cylinder, asecond arm having a projection thereon secured to the other end of saidsecond shaft within said housing adapted to rotate said second shaft,conduit means leading from the space between the said piston and theclosed end of said cylinder and communicating with a source of enginesuction, second conduit means leading from the said housing andcommunicatingwith a source of heated air at substantially atmosphericpressure, thermostatic means within said housing adapted to bias saidprojection in a direction so as to close said choke valve, connectingmeans including a lost motion coupling therein between said second armand said piston enabling said piston to oppose the movement of saidthermostat whenever said engine is running, and a thermostaticallycontrolled stop member between said piston and said closed end of saidcylinder for limiting the degree of opposition by said piston.

7. In a carburetor for internal combustion engines, a choke valve, meansincluding a heat responsive device to close said choke valve at lowtemperatures, a device responsive to engine suction for causing at leasta partial opening of said choke valve against the tension of said heatresponsive device upon starting of the engine, and abutment meansassociated with and adapted to limit the movement of said suctionresponsive device in order to limit the amount of choke opening due tosaid suction responsive device, said abutment means comprising a firstexternally threaded member rigidly secured to said carburetor, a secondinternally threaded member adapted to cooperate with said first memberin a manner 15 2,818,239

so as to provide for relative axial movement between said first andsecond members, a thermostatic element coiled about said second memberand having one of its ends secured to said second member, and an anchormember rigidly mounted to said carburetor and adapted to retain theother end of said thermostatic element thereby allowing saidthermostatic element to cause axial adjustment of said first memberrelative to said second member in accordance with temperature.

References Cited in the file of this patent UNITED STATES PATENTS OlsonDec. 31, 1957 Eickmeier et al Dec. 31, 1957

